1. Field of the Invention
The present invention relates to a light source apparatus which supplies illuminating light to a medical endoscope inserted into a subject for observing a tissue in a body and an endoscope system having the light source apparatus, and more particularly, to a light source apparatus that supplies illuminating light for white light imaging and special light imaging, and an endoscope system having the light source apparatus.
2. Description of the Related Art
Since sites to be observed are located inside a living body, medical endoscopes require a light source apparatus for illuminating the interior of the body. Illuminating light generated by the light source apparatus illuminates a target tissue from a distal end portion where an image pickup section is located via a light guide which is inserted into an insertion portion of the endoscope.
As for imaging using an endoscope, normal light imaging using visible light (white light imaging: WLI) is generally performed and various kinds of special light imaging utilizing wavelength characteristics of irradiating light are also performed.
For example, Japanese Patent Application Laid-Open Publication No. 2007-29453 discloses a frame-sequential endoscope system to perform narrow band imaging, auto fluorescence imaging and infrared imaging or the like as special light imaging.
In narrow band imaging (NBI), in order to observe blood vessels with high contrast, with attention focused on the utilization of light that has features of being strongly absorbed by blood as well as being strongly reflected/scattered by the mucosal epithelium, blue narrow band light and green narrow band light are sequentially radiated to thereby highlight the contrast between the capillary vessel of the mucosal epithelium and a deep thick blood vessel.
In auto fluorescence imaging (AFI), excitation light for observing fluorescence from a fluorescent substance such as collagen and light of a wavelength absorbed by hemoglobin in the blood are sequentially radiated to highlight a tumorous lesion and a normal mucous membrane with different color tones.
In infrared imaging (IRI), indocyanine green (ICG) through which infrared light is easily absorbed is intravenously injected and two infrared light beams having different wavelengths are sequentially radiated to thereby highlight a blood vessel of the deep mucous membrane which is not easily recognizable to human eyes and blood flow information.
Japanese Patent Application Laid-Open Publication No. 2007-29453 discloses the use of irradiating light passing through a normal red, green or blue primary color filter and a filter that passes light of a relatively wide wavelength band to prevent damage to an endoscope by heat of infrared light.